1. Field of the Invention
The present invention relates generally to improved methods of preventing well fracture proppant flow-back, and more particularly, to improved methods of fracturing a subterranean zone and propping the fractures whereby proppant flow-back from the fractures is prevented.
2. Description of the Prior Art
Oil and gas wells are often stimulated by hydraulically fracturing subterranean producing zones penetrated thereby. In such hydraulic fracturing treatments, a viscous fracturing fluid is pumped into the zone to be fractured at a rate and pressure such that one or more fractures are formed and extended in the zone. A solid particulate material for propping the fractures open, referred to herein as "proppant," is suspended in a portion of the fracturing fluid so that the proppant is deposited in the fractures when the viscous fracturing fluid is caused to revert to a thin fluid and returned to the surface. The proppant functions to prevent the fractures from closing whereby conductive channels are formed through which produced fluids can readily flow.
In order to prevent the subsequent flow-back of the proppant as well as subterranean formation particulate solids with fluids produced from the fractured zone, at least a portion of the proppant has heretofore been coated with a hardenable resin composition and consolidated into a hard permeable mass. Typically, the resin composition coated proppant is deposited in the fractures after a larger quantity of uncoated proppant material has been deposited therein. That is, the last portion of the proppant deposited in each fracture, referred to in the art as the "tail-in" portion, is coated with a hardenable resin composition. Upon the hardening of the resin composition, the tail-in portion of the proppant is consolidated into a hard permeable mass having a high compressive strength whereby unconsolidated proppant and formation particulate solids are prevented from flowing out of the fractures with produced fluids. While this technique has been successful, the high costs of the hardenable resin composition and the mixing and proppant coating procedures utilized have contributed to making the cost of the fracturing procedure very high.
Recently, fibers have been mixed with the proppant and the mixture has been deposited in fractures. The fibers function to inhibit the flow-back of proppant by filling channels or void spaces in the proppant pack with fibers thereby inhibiting the movement of proppant and formation particulate solids through the propped fracture. While the presence of the fibers has successfully reduced proppant flow-back in some applications, in others both proppant as well as fibers flow out of the fractures with produced fluids causing damage and operational problems to well production and processing equipment.
Thus, there is a need for improved methods of fracturing and placing proppant in subterranean zones whereby the flow-back of proppant with produced fluids is prevented.